Facebook Holders Tighten Their Grip

Facebook Inc. took steps to solidify the control of founder Mark Zuckerberg and other existing shareholders in the event the social-networking company goes public.

The closely held Silicon Valley firm, emulating one of Google Inc.'s well-known strategies, established a dual-class stock structure that would increase the voting power of Mr. Zuckerberg, who is the company's chief executive, and other existing shareholders if they hold...